WO2014030904A1 - Method and device for transmitting channel state information in wireless communication system - Google Patents

Abstract

The present invention relates to a wireless communication system. A method for transmitting channel state information (CSI) by a user equipment (UE) in a wireless communication system, according to one embodiment of the present invention, can comprise the steps of: receiving a CSI reference signal (CSI-RS); determining an overhead of a common reference signal (CRS) resource element on the basis of the number of antenna ports which is the same number of antenna ports associated with the CSI-RS; and transmitting the CSI calculated on the basis of the CSI-RS and the overhead of the CRS resource element.

Description

[Specification] ^'

 [Name of invention]

 Method and apparatus for transmitting channel state information (CSI) in wireless communication system

 Technical Field

 [1] The present invention relates to a wireless communication system, and more particularly, to determine a common reference signal (CRS) overhead and calculate channel state information in a wireless communication system supporting Cooperative Multipoint (CoMP). The present invention relates to a method and apparatus for transmitting channel state information.

 Background Art

 [2] Multi-Input Multi-Output (MIMO) technology improves the efficiency of data transmission and reception by using multiple transmit antennas and multiple receive antennas, eliminating the use of one transmit antenna and one receive antenna. Technology. If a single antenna is used, the receiving side receives data through a single antenna path, but if multiple antennas are used, the receiving end receives data through several paths. Therefore, the data transfer rate can be improved-the amount of transmission can be improved, and the coverage can be increased.

 [3] Single-cell MIM0 operation includes a single user-MIMO (SU-MIM0) scheme in which one UE receives a downlink signal in one cell, and two or more UEs perform one operation. Multi-user MIMO (MIHIIMO) scheme for receiving a downlink signal in a cell may be divided.

 On the other hand, research on a coordinated multi-point (CoMP) system for improving throughput of a user at a cell boundary by applying an improved MIM0 transmission in a multi-cell environment is being actively conducted. CoMP system can reduce inter-cell interference and improve the overall system performance in multi-cell cell environment.

[5] Channel estimation refers to a process of restoring a received signal by compensating for distortion of a signal caused by fading. Here, fading is a multipath in a wireless communication system environment. This is a phenomenon in which the strength of a signal fluctuates rapidly due to time delay. For channel estimation, a reference signal known to both the transmitter and the receiver is required. Also, the reference signal is simply It may also be referred to as a pilot (Pi lot) depending on RS (Reference Signal) or applicable standard.

 [6] The downlink reference signal is a coherent such as a Physical Downlink Shared CHannel (PDSCH), a Physical Control Format Indicator CHannel (PCFICH), a Physical Hybrid Indicator CHannel (PHICH), and a Physical Downlink Control CHannel (PDCCH). (coherent) Pilot signal for demodulation. The downlink reference signal includes a common reference signal (CRS) shared by all terminals in a cell and a dedicated reference signal (DRS) dedicated to a specific terminal. Conventional communication systems supporting 4 transmit antennas (e.g., systems according to the LTE release 8 or 9 standard) have systems with extended antenna configurations (e.g., LTE- supporting 8 transmit antennas). In the system according to A standard, DRS-based data demodulation is considered to support efficient reference signal operation and advanced transmission scheme. That is, DRSs for two or more layers may be defined to support data transmission through an extended antenna. Since the DRS is precoded by the same precoder as the data, the channel information for demodulating data at the receiving side can be easily estimated without any separate coding information.

 On the other hand, while the downlink receiving side can obtain precoded channel information for the extended antenna configuration through the DRS, a separate reference signal other than the DRS is required to obtain uncoded channel information. . Accordingly, in the system according to the LTE-A standard, a reference signal for acquiring channel state information (CSI) may be defined at a receiving side, that is, CSI ᅳ RS.

 [Detailed Description of the Invention]

[Technical problem]

Based on the above discussion, a method and apparatus for reporting channel state information in a wireless communication system will now be proposed.

 [9] The technical problems to be achieved in the present invention are not limited to the above technical problems, and other technical problems not mentioned will be clearly understood by those skilled in the art to which the present invention belongs from the following description. Could be.

Technical Solution In order to solve the above problem, a method of transmitting channel state information (CSI) by a terminal in a wireless communication system according to an embodiment of the present invention includes receiving a channel state information-reference signal (CSI-RS). Doing; Determining an overhead of a common reference signal (CRS) resource element based on the same antenna port number as the antenna port number associated with the CSI-RS; And transmitting the channel state information calculated based on the overhead of the CSI—RS and the CRS resource element.

 In a wireless communication system according to another embodiment of the present invention, a method for receiving channel state information (CSI) by a base station includes: transmitting channel state information ᅳ reference signal (CSI-RS); And receiving the channel state information calculated based on an overhead of a CRS resource element and the CSI-RS, wherein the overhead of the CRS resource element is equal to the number of antenna ports associated with the CSI-RS. Determined based on the number of ports.

 [12] A terminal for transmitting channel state information (CSI) in a wireless communication system according to another embodiment of the present invention includes: a RKRadio Frequency unit; And a processor, wherein the processor receives a channel state information_reference signal (CSI_RS) and is based on a common reference signal (CRS) resource based on the same antenna port number as the number of antenna ports associated with the CSI-RS. It is configured to determine the overhead of the element and to transmit the channel state information calculated based on the overhead of the CSI RS and the CRS resource element.

 A base station for receiving channel state information (CSI) in a wireless communication system according to another embodiment of the present invention includes: a radio frequency (I ^) unit; And a processor, wherein the processor transmits a channel state information ᅳ reference signal (CSI-RS), receives the channel state information calculated based on an overhead of a CRS resource element and the CSI-RS, The overhead of the CRS resource element is configured to be determined based on the same antenna port number as the antenna port number associated with the CSI-RS.

 [14] The following matters may be applied to embodiments of the present invention in common.

 [15] The method may further include receiving CSI configuration information for reporting the CSI.

 The CSI configuration information may be configured to report a channel quality indicator (CQI) without reporting a precoding matrix indicator (PMI) and a rank indicator (RI).

The CSI configuration information may be transmitted through RRC (Radio Resource Control) signaling. [18] The antenna port number associated with the CSI—RS may be set to 4 or less.

 The CSI may indicate a channel state in a cooperative multi-point (CoMP) time division (TDD) system that satisfies channel reciprocity.

 The foregoing general description of the invention and the following detailed description are exemplary and intended to provide further explanation of the invention as set forth in the claims.

 Advantageous Effects

According to an embodiment of the present invention, channel state information may be more effectively reported in a wireless communication system.

 In addition, according to an embodiment of the present invention, in a wireless communication system supporting Cooperative Multipoint (CoMP), channel overhead information may be calculated by efficiently determining a common reference signal (CRS) overhead. Can be.

 [23] Effects obtained in the present invention are not limited to the above-mentioned effects, and other effects not mentioned above are clearly described to those skilled in the art from the following description. It can be understood.

 [Brief Description of Drawings]

The accompanying drawings, which are included as a part of the detailed description to help understand the present invention, provide an embodiment of the present invention, and together with the detailed description, describe the technical idea of the present invention.

 1 is a diagram illustrating a structure of a downlink radio frame.

 [26] FIG. 2 shows an example of a resource grid for one downlink slot.

 3 shows a structure of a downlink subframe.

 4 illustrates a structure of an uplink subframe.

 5 is a configuration diagram of a wireless communication system having multiple antennas.

 FIG. 6 is a diagram illustrating patterns of existing CRSs and DRSs.

 FIG. 7 is a diagram illustrating an example of a DM RS pattern. FIG.

 8 is a diagram illustrating an example of a CSI—RS pattern.

9 is a diagram for explaining an example of a method in which a CSI-RS is periodically transmitted. 10 is a diagram for explaining an example of a method in which a CSI-RS is transmitted aperiodically.

 FIG. 11 illustrates an example in which two CSI-RS configurations are used.

 12 is a flowchart illustrating a method of transmitting channel state information according to an embodiment of the present invention.

 FIG. 13 is a diagram illustrating a configuration of a base station and a terminal that can be applied to an embodiment of the present invention. FIG.

 BEST MODE FOR CARRYING OUT THE INVENTION The following embodiments combine the components and features of the present invention in a predetermined form. Each component or feature may be considered optional unless stated otherwise. Each component or feature may be implemented in a form that is not combined with other components or features. In addition, some of the components and / or features may be combined to form an embodiment of the present invention. The order of the operations described in the embodiments of the present invention may be changed. Some components or features of one embodiment may be included in another embodiment or may be replaced with corresponding components or features of another embodiment.

 Embodiments of the present invention will be described with reference to the relationship between data transmission and reception between a base station and a terminal. Here, the base station has a meaning as a terminal node of the network that directly communicates with the terminal. The specific operation described as performed by the base station in this document may be performed by an upper node of the base station in some cases.

That is, it is obvious that various operations performed for communication with a terminal in a network including a plurality of network nodes including a base station may be performed by the base station or network nodes other than the base station. Do. A 'base station (BS)' may be replaced by terms such as a fixed stat ion, a Node B, an eNode B (eNB), and an access point (AP). The repeater may be replaced by other terms such as relay node (RN) and relay station (RS). In addition, the term 'terminal' may be replaced with terms such as a user equipment (UE), a mole le station (MS), a mole le subscriber station (MSS), and a subscribing station (SS). Specific terms used in the following description are provided to help the understanding of the present invention, and the use of the specific terms may be changed to other forms without departing from the technical spirit of the present invention.

 In some cases, in order to avoid obscuring the concepts of the present invention, well-known structures and devices may be omitted or shown in block diagram form centering on the core functions of the structures and devices. In addition, the same components will be described with the same reference numerals throughout the present specification.

 Embodiments of the present invention may be supported by standard documents disclosed in at least one of the IEEE 802 system, the 3GPP system, the 3GPP LTE and the LTE-A (LTE-Advanced) system, and the 3GPP2 system, which are wireless access systems. That is, steps or parts which are not described to clearly reveal the technical spirit of the present invention among the embodiments of the present invention may be supported by the above documents. In addition, all the terms disclosed in this document can be described by the standard document.

The following techniques are code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (0FDMA), and single carrier frequency (SC-FDMA). Division Mult iple Access) and the like can be used in various wireless access systems. CDMA may be implemented by a radio technology such as Universal Terrestrial Radio Access (UTRA) or CDMA2000. TDMA may be implemented in a wireless technology such as Global System for Mobile communication (GSM) / Gener a 1 Packet Radio Service (GPRS) / Enhanced Data Rates for GSM Evolut ion (EDGE). 0FDMA may be implemented with a radio technology such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, Evolved UTRA (E-UTRA). UTRA is part of the UMTSCUniversal Mobile Telecommunications System. 3rd Generation Partnership Project (3GPP) long term evolut ion (LTE) is part of Evolved UMTS (E-UMTS) using E-UTRA, and employs 0FDMA in downlink and SC-FDMA in uplink. LTE—A (Advanced) is an evolution of 3GPP LTE. WiMAX can be described by the IEEE 802.16e standard (WirelessMAN-OFDMA Reference System) and the advanced IEEE 802.16m standard (WirelessMAN-OFDMA Advanced system). For clarity, the following description focuses on the 3GPP LTE and LTE-A standards, but the technical spirit of the present invention is not limited thereto. . A structure of a downlink radio frame will be described with reference to FIG. 1.

 In a cellular OFDM wireless packet communication system, uplink / downlink data packet transmission is performed in subframe units, and one subframe is defined as a predetermined time interval including a plurality of OFDM symbols. The 3GPP LTE standard supports a type 1 radio frame structure applicable to frequency division duplex (FDD) and a type 2 radio frame structure applicable to time division duplex (TDD).

FIG. 1 is a diagram illustrating a structure of a type 1 radio frame. The downlink radio frame consists of 10 subframes, and one subframe consists of two slots in the time domain. The time it takes for one subframe to be transmitted is called a TTKtransmission time interval). For example, one subframe may have a length of 1 ms, and one slot may have a length of 0.5 ms. One slot includes a plurality of 0FDM symbols in the time domain and a plurality of Resource Blocks (RBs) in the frequency domain. Since the 3GPPLTE system uses 0FDMA in downlink, the 0FDM symbol is one symbol interval. The 0 FDM symbol may also be referred to as an SC-FDMA symbol or symbol interval. A resource block (RB) is a resource allocation unit and may include a plurality of consecutive subcarriers (s _L1 bcarriers) in one slot.

 The number of 0FDM symbols included in one slot may vary depending on the configuration of CPCCyclic Prefix). CPs include extended CPs and normal CPC normal CPs. For example, when the 0FDM symbol is configured by a general CP, the number of 0FDM symbols in one slot may be seven. When the 0FDM symbol is configured by an extended CP, the length of one 0FDM symbol is increased. The number of 0FDM symbols included in one slot is smaller than that of the normal CP. In the case of an extended CP, for example, the number of 0FDM symbols included in one slot may be six. If the channel state is unstable, such as when the terminal moves at a high speed, an extended CP may be used to further reduce intersymbol interference.

When a normal CP is used, since one slot includes 7 OFDM symbols, one subframe includes 14 0FDM symbols. In this case, the first two or three 0FDM symbols of each subframe may be allocated to a physical downlink control channel (PDCCH), and the remaining 0FDM symbols may be allocated to a physical downlink shared channel (PDSCH). The structure of the radio frame is merely an example, and the number of subframes included in the radio frame, the number of slots included in the subframe, and the number of symbols included in the slot may be variously changed.

 2 illustrates an example of a resource grid for one downlink slot. This is a case where the OFDM symbol is composed of a normal CP. Referring to FIG. 2, the downlink slot includes a plurality of OFDM symbols in the time domain and includes a plurality of resource blocks in the frequency domain. Here, one downlink slot includes 7 OFDM symbols and one resource block includes 12 subcarriers as an example. However, the present invention is not limited thereto. Each element on the resource grid is called a resource element (RE). For example, the resource element a (k, l) becomes a resource element located in the k th subcarrier and the first 0FDM symbol. In the case of a normal CP, one resource block includes 12X7 resource elements (in the case of an extended CP, 12X6 resource elements). Since the interval of each subcarrier is 15 kHz, one resource block includes about 180 kHz in the frequency domain. NDL is the number of resource blocks included in a downlink slot. The value of NDL may be determined according to the downlink transmission bandwidth set by scheduling of the base station.

3 shows a structure of a downlink subframe. Up to three 0FDM symbols in the front of the first slot in one subframe correspond to the control region to which the control channel is allocated. The remaining 0FDM symbols correspond to a data area to which a Physical Downlink Shared Chancel (PDSCH) is allocated. The basic unit of transmission is one subframe. That is, downlink control channels used in a D-.3GPP LTE system in which PDCCH and PDSCH are allocated over two slots include, for example, a physical control format indicator channel (PCFICH), Physical Downlink Control Channel (PDCCH), Physical HARQ Indicator Channel (PHICH), and the like. The PCFICH is transmitted in the first 0FDM symbol of a subframe and includes information on the number of OFDM symbols used for control channel transmission in the subframe. The PHICH includes a HARQACK / NACK signal as a response of uplink transmission. Control information transmitted through the PDCCH is referred to as downlink control information (DCI). The DCI includes uplink or downlink scheduling information or includes an uplink transmit power control command for a certain terminal group. PDCCH is a resource allocation and transmission format of the DL-SCH. Information of a higher layer control message such as resource allocation information of an uplink shared channel (UL-SCH), paging information of a paging channel (PCH), system information on a DL-SCH, and a random access response transmitted on a PDSCH. Resource allocation, a set of transmit power control commands for individual terminals in an arbitrary terminal group, transmit power control information, activation of Voice over IP (VoIP), and the like. A plurality of PDCCHs may be transmitted in the control region. The terminal may monitor the plurality of PDCCHs. The PDCCH is transmitted in a combination of one or more consecutive Control Channel Elements (CCEs). CCE is a logical allocation unit used to provide a PDCCH at a coding rate based on the state of a radio channel. The CCE processes multiple resource element groups. The format of the PDCCH and the number of available bits are determined according to the correlation between the number of CCEs and the coding rate provided by the CCEs. The base station determines the PDCCH format according to the DCI transmitted to the terminal, and adds a Cyclic Redundancy Check (CRC) to the control information. The CRC is masked with an identifier called Radio Network Temporary Identifier (RNTI) according to the owner or purpose of the PDCCH. PDCCH 7} In case of a specific UE, the cell-RNTI (C-RNTI) identifier of the UE may be masked in the CRC. Alternatively, if the PDCCH is for a paging message, a paging indicator identifier (P-RNTI) may be masked to the CRC. If the PDCCH is for system information (more specifically, system information block (SIB)), the system information identifier and system information RNTI (SI—RNTI) may be masked to the CRC. In order to indicate a random access response that is a response to the transmission of the random access preamble of the UE, the random access RNTI (RA-RNTI) may be masked to the CRC.

4 shows a structure of an uplink subframe. The uplink subframe may be divided into a control region and a data region in the frequency domain. In the control region, a physical uplink control channel (PUCCH) including uplink control information is allocated. In the data area, a physical uplink shared channel (PUSCH) including user data is allocated. In order to maintain a single carrier characteristic, one UE does not simultaneously transmit a PUCCH and a PUSCH. PUCCH for one UE is allocated to an RB pair in a subframe. Resource blocks belonging to the resource block pair occupy different subcarriers for two slots. This is called a resource block pair allocated to the PUCCH is frequency-hopped at the slot boundary. [54] Modeling of Multiple Antenna (MIMO) Systems

 [55] The Multiple Input Multiple Output (MIM0) system is a system that improves the transmission and reception efficiency of data by using multiple transmission antennas and multiple reception antennas.MIM0 technology does not rely on a single antenna path to receive an entire message. The entire data may be received by combining a plurality of pieces of data received through a plurality of antennas.

 [56] The MIM0 technology includes a spatial diversity technique and a spatial multiplexing technique. Spatial diversity scheme can increase transmission reliability or cell radius through diversity gain, and is suitable for data transmission for a mobile terminal moving at high speed. Spatial multiplexing can increase the data rate without increasing the bandwidth of the system by simultaneously transmitting different data.

 5 is a configuration diagram of a wireless communication system having multiple antennas. As shown in FIG. 5 (a), when the number of transmitting antennas is increased to NT and the number of receiving antennas is increased to NR, the theoretical channel is proportional to the number of antennas, unlike when only a plurality of antennas are used in a transmitter or a receiver The transmission capacity is increased. Therefore, the transmission rate can be improved and the frequency efficiency can be significantly improved. As the channel transmission capacity is increased, the transmission rate may theoretically increase as the rate of increase rate Ri multiplied by the maximum transmission rate Ro when using a single antenna.

[58] [Equation 1] [59] ^ = min (^ V ₇ , Vj

 For example, in a MIM0 communication system using four transmitting antennas and four receiving antennas, a transmission rate four times higher than a single antenna system may be theoretically obtained. Since the theoretical increase in capacity of multi-antenna systems was proved in the mid-90s, various techniques have been actively studied to bring this to substantial data rate improvement. In addition, some technologies are already being reflected in various wireless communication standards such as 3G mobile communication and next generation WLAN.

[61] Looking at the trends related to multi-antenna research to date, the study of information theory aspects related to the calculation of multi-antenna communication capacity in various channel environment and multi-access environment, the study of wireless channel measurement and model derivation of multi-antenna system, transmission reliability Enhance and transfer Research is being actively conducted from various perspectives, such as research on space-time signal processing technology for improvement.

 [62] The method of communication in a multi-antenna system is described in more detail using mathematical modeling. In the system, it is assumed that NT and transmit antennas and NR receive antennas exist.

 [63] Referring to the transmission signal, if there are NT transmission antennas, the maximum information that can be transmitted is NT. The transmission information may be expressed as follows.

 [64] [Equation 2]

S

[65] ^S \ ， ^S 2 ： N _r J

In each transmission information, ^ may have a different transmission power. Each full power adjusted transmission information is as follows.

[67] [Equation 3]

 In addition, S may be expressed as follows using the diagonal matrix P of the transmission power.

 [70] [Equation 4]

[72] Consider a case where NT transmission signals, ² , ^' ᅳ ^' , and _r are actually formed by applying an augmentation matrix W to an information vector S whose transmission power is adjusted. The weighting matrix W plays a role in properly distributing transmission information to each antenna according to a transmission channel situation. ， ^ ² ， ^''' » ^" \ ^ can be expressed using vector X as

[73] [Equation 5] Ws-WPs

Here, ¹ means an increment between the i th transmit antenna and the j th information. W is also called a precoding matrix.

 On the other hand, the transmission signal X may be considered in different ways depending on two cases (eg, spatial diversity and spatial multiplexing). In the case of spatial multiplexing, different signals are multiplexed and the multiplexed signal is transmitted to the receiver, so that elements of the information vector (s) have different values. On the other hand, in the case of spatial diversity, the same signal is repeatedly transmitted through a plurality of channel paths so that the elements of the information vector (s) have the same value. Of course, a combination of spatial multiplexing and spatial diversity techniques can also be considered. That is, the same signal may be transmitted according to a spatial diversity scheme through three transmission antennas, for example, and the remaining signals may be spatially multiplexed and transmitted to a receiver.

 When there are NR receiving antennas, the received signals of each antenna, ^^, ^^, may be expressed as vectors as follows.

[78] [Equation 6]

 When modeling a channel in a multi-antenna wireless communication system, channels may be classified according to transmit / receive antenna indexes. The signal passing through the receiving antenna i from the transmitting antenna j is denoted by " ϋ. Note that, in ^, the order of the index-the receiving antenna index is first, and the index of the transmitting antenna is later.

 FIG. 5 (b) shows a channel from NT transmit antennas to receive antenna i. The channels may be bundled and displayed in the form of a vector and a matrix. In FIG. 5 (b), a channel arriving from a total of NT transmit antennas to a receive antenna i may be represented as follows.

[82] [Equation 71

 Accordingly, all channels arriving from the NT transmit antennas to the NR receive antennas may be expressed as follows.

 [85] r [8]

 [87] In real channel, after passing through the channel matrix H, white noise (GN) is added.

Gaussian Noise is added. The white noise " '·· " " ^ added to each of the NR receive antennas can be expressed as follows.

[88] [Equation 9] η = [η _ι , η ₂ , ·-·, η _Νκ }

L [889J] L ^{^} i ', N _R J

 [[9900]] The received signal can be expressed as follows through the imaginary mathematical modeling ring.

 [91] [Equation 10]

[92]

 [[9933]] The number of rows and columns of the channel matrix H representing the channel state is determined by the number of transmit / receive antennas. The number of rows is equal to the number of receiving antennas NR, and the number of columns is equal to the number of transmitting antennas NT. That is, the channel matrix H is NRXNT matrix.

 A rank of a matrix is defined as the minimum number of rows or columns that are independent of each other. Thus, the tank of the matrix cannot be larger than the number of rows or columns. The rank of the channel matrix H (rawfe (H)) is limited as follows.

[95] [Equation 11] [96] rank R) ≤ min (iV _r , N _R )

 In MIMO transmission, 'rank' indicates the number of paths that can independently transmit a signal, and 'number of layers' indicates the number of signal streams transmitted through each path. In general, since the transmitting end transmits the number of layers corresponding to the number of hanks used for signal transmission, unless otherwise specified, the tank has the same meaning as the number of layers.

 [98] Reference Signal (RS)

 In the wireless communication system, a packet is transmitted. Since a transmitted packet is transmitted through a wireless channel, signal distortion may occur during the transmission process. In order to correctly receive the distorted signal at the receiving end, the distortion must be corrected in the received signal using the channel information. In order to find out the hard channel information, the signal transmitted by both the transmitting side and the receiving side is transmitted. It is mainly used to find channel information with the degree of distortion when it is received through the channel. The signal is called a pilot signal or a reference signal.

 In case of transmitting / receiving data using multiple antennas, it is necessary to know the channel condition between each transmitting antenna and the receiving antenna to receive the correct signal. Therefore, a separate reference signal must exist for each transmitting antenna.

 In a mobile communication system, RSs can be classified into two types according to their purpose. One is an RS used for channel information acquisition, and the other is an RS used for data demodulation. Since the former is an RS for allowing the terminal to acquire downlink channel information, the former should be transmitted over a wide band, and a terminal that does not receive downlink data in a specific subframe should be able to receive and measure the corresponding RS. Such RS is also used for measurement such as handover. The latter is an RS that is transmitted together with the corresponding resource when the base station transmits a downlink, and the terminal can estimate the channel by receiving the corresponding RS, and thus can demodulate the data. This RS should be transmitted in the area where data is transmitted.

In the existing 3GPP LTE (eg, 3GPP LTE Release-8) system, two types of downlink RSs are defined for unicast services. One of them is a common reference signal (Co 隱 on RS; CRS), and the other is a dedicated RS (DRS). CRS is for obtaining information about channel status and measuring for handover May be used and may be referred to as cell-specific RS. The DRS is used for data demodulation and may be called a UE-specific RS. In the existing 3GPPLTE system, DRS is used only for data demodulation, and CRS can be used for both purposes of channel information acquisition and data demodulation.

 The CRS is a cell-specific RS and is transmitted every subframe for a wideband. The CRS can be transmitted for up to four antenna ports depending on the number of transmit antennas in the base station. For example, if the number of transmit antennas of the base station is two, CRSs for antenna ports 0 and 1 are transmitted, and if four, CRSs for antenna ports 0 to 3 are transmitted.

6 shows a pattern of CRS and DRS on one resource block (12 subcarriers on 14 OFDM symbols X frequencies in time in case of a normal CP) in a system in which a base station supports four transmit antennas. Drawing. In FIG. 6, resource elements RE denoted as' R0 ¹ , 'Rl', 'R2' and 'R3' indicate positions of CRSs for antenna port indexes 0, 1, 2, and 3, respectively. Meanwhile, a resource element denoted as 'D' in FIG. 6 indicates a position of a DRS defined in an LTE system.

Evolution of the LTE System In the advanced LTE-A system, up to eight transmit antennas can be supported in downlink. Therefore, RS for up to eight transmit antennas must also be supported. Since the downlink RS in the LTE system is defined only for up to four antenna ports, in the LTE-A system, if the base station has up to 8 downlink transmit antennas over 4 7) 1, the RS for these antenna ports is ^It handi be defined further. As RS for up to eight transmit antenna ports, both RS for channel measurement and RS for data demodulation should be considered.

[106] One of the important considerations when designing an LTE-A system is backward compatibility. Backward compatibility means that existing LTE terminals support LTE-A system operation correctly. From the RS transmission point of view, if the RS for the maximum 8 transmit antenna ports is added to the time-frequency domain where CRS defined in the LTE standard is transmitted every subframe over the entire band, the RS overhead becomes excessively large. do. Therefore, in designing RS for up to 8 antenna ports, consideration should be given to reducing RS overhead. RS newly introduced in the LTE-A system can be classified into two types. One of them is RS in channel state information for the purpose of channel measurement for the selection of transmission rank, modulation and coding scheme (MCS), precoding matrix index (PMI), etc. State Information RS (CSI-RS), and the other is a demodulation-reference signal (DM RS), which is an RS for demodulating data transmitted through up to eight transmit antennas.

 [108] CSI-RS for channel measurement purpose is different from CRS in LTE system, which is used for data demodulation at the same time as channel measurement and handover measurement. There is a feature to be designed. Of course, the CSI-RS may also be used for the purpose of measuring handover. Since the CSI-RS is transmitted only for obtaining channel state information, unlike the CRS in the existing LTE system, the CSI-RS does not need to be transmitted every subframe. Thus, to reduce the overhead of the CSI-RS, the CSI-RS may be designed to be transmitted intermittently (eg, periodically) on the time axis.

 [109] If on some downlink subframe. When data is transmitted, a dedicated DM RS is transmitted to a terminal scheduled for data transmission. The DM RS dedicated to a specific terminal may be designed to be transmitted only in a resource region in which the terminal is scheduled, that is, a time in which data for the terminal is transmitted—frequency region.

FIG. 7 is a diagram illustrating an example of a DM RS pattern defined in an LTE-A system. FIG. 7 shows positions of resource elements for transmitting a DM RS on one resource block in which downlink data is transmitted (12 subcarriers over 14 0FDM symbol X frequencies in time in case of a general CP). The DM RS may be transmitted for four antenna ports (antenna port indexes 7, 8, 9, and 10) which are additionally defined in the LTE-A system. DM RSs for different antenna ports can be distinguished by being located in different frequency resources (subcarriers) and / or different time resources (0 FDM symbols) (ie, can be multiplexed in FDM and / or TDM schemes). . In addition, DM RSs for different antenna ports located on the same time-frequency resource may be distinguished from each other by orthogonal codes (ie, multiplexed in the CDM manner). In the example of FIG. 7, DM RSs for antenna ports 7 and 8 may be located in resource elements (REs) indicated as DMRSCDM group 1, and they may be multiplexed by an orthogonal code. Similarly, DM RS group 2 in the example of FIG. In the resource elements denoted by DM RSs for antenna ports 9 and 10 may be located, they may be multiplexed by an orthogonal code.

 8 is a diagram illustrating examples of a CSI-RS pattern defined in an LTE-A system. FIG. 8 shows the location of a resource element on which a CSI-RS is transmitted on one resource block in which downlink data is transmitted (12 subcarriers on 14 OFDM symbols X frequencies in time in the case of a general CP). In any downlink subframe, one of the CSI-RS patterns of FIGS. 8 (a) to 8 (e) may be used. The CSI-RS may be transmitted for eight antenna ports (antenna port indexes 15, 16, 17., 18, 19, 20, 21, and 22) which are additionally defined in the LTE-A system. CSI-RSs for different antenna ports can be distinguished by being located in different frequency resources (subcarriers) and / or different time resources (OFDM symbols)-(ie, can be multiplexed in FDM and / or TDM schemes). ). In addition, CSI-RSs for different antenna ports located on the same time-frequency resource may be distinguished from each other by orthogonal codes (ie, multiplexed in the CDM scheme). In the example of FIG. 8 (a), CSI-RSs for antenna ports 15 and 16 may be located in resource elements (REs) designated as CSI-RS CDM group 1, which may be multiplexed by an orthogonal code. In the example of FIG. 8 (a), CSI-RSs for antenna ports 17 and 18 may be located in resource elements indicated as CSI-RS CDM group 2, which may be multiplexed by an orthogonal code. In the example of FIG. 8A, CSI-RSs for antenna ports 19 and 20 may be located in resource elements indicated as CSI-RS CDM group 3, which may be multiplexed by an orthogonal code. In the resource elements indicated as CSI-RS CDM group 4 in the example of FIG. 8 (a), CSI-RSs for antenna ports 21 and 22 may be located, and they may be multiplexed by an orthogonal code. The same principle described with reference to FIG. 8 (a) can be applied to FIGS. 8 (b) to 8 (e).

 6 to 8 are merely exemplary and are not limited to a specific RS pattern in applying various embodiments of the present disclosure. That is, even when RS patterns different from those of FIGS. 6 to 8 are defined and used, various embodiments of the present invention may be equally applied.

 [113] Cooperative Mult i-Point (CoMP)

[114] Depending on the improved system performance requirements of the 3GPP LTE-A system, CoMP transceiver technology (also referred to as co-MIM0, collaborative MIM0 or network MIM0, etc.) Is being proposed. CoMP technology can increase the performance of the terminal located in the cell-edge and increase the average sector throughput.

 [115] In general, in a multi-sal environment with a frequency reuse factor of 1, the performance and average sector yield of a terminal located in a cell boundary due to inter-cell interference (ICI) This can be reduced. To reduce this ICI, existing LTE systems use cell-boundary in an environment constrained by interference using simple passive techniques such as fractional frequency reuse (FFR) through UE-specific power control. A method for ensuring that a terminal located at has a proper yield performance has been applied. However, rather than reducing the use of frequency resources per cell, it may be more desirable to reduce the ICI or reuse the ICI as a signal desired by the terminal. In order to achieve the above object, CoMP transmission scheme can be applied.

 CoMP schemes applicable to downlink can be classified into joint processing (JP) techniques and coordinated scheduling I beamforming (CS / CB) techniques.

 The JP technique may use data at each point (base station) of the CoMP cooperative unit. CoMP cooperative unit means a set of base stations used in a cooperative transmission scheme. The JP technique can be classified into a joint transmission technique and a dynamic cell selection technique.

 The joint transmission scheme refers to a scheme in which PDSCH is transmitted from a plurality of points (part or all of CoMP cooperative units) at a time. That is, data transmitted to a single terminal may be simultaneously transmitted from a plurality of transmission points (TPs). According to the joint transmission technique, the quality of a received signal can be improved coherently or non-coherent ly, and can also actively cancel interference with other terminals. .

The dynamic cell selection scheme refers to a scheme in which PDSCHs are transmitted from one point (of CoMP cooperative units) at a time. That is, data transmitted to a single terminal at a specific point in time is transmitted from one point, and other points in the cooperative unit do not transmit data to the corresponding terminal at that point, and the point for transmitting data to the corresponding terminal is dynamically Can be selected. Meanwhile, according to the CS / CB technique, CoMP cooperative units may cooperatively perform beamforming of data transmission for a single terminal. Here, although data is transmitted only in the serving cell, user scheduling / beamforming may be determined by coordination of cells of a corresponding CoMP cooperative unit.

 Meanwhile, in the uplink case, coordinated multi-point reception means receiving a signal transmitted by coordination of a plurality of geographically separated points. CoMP schemes applicable to uplink can be classified into joint reception (JR) and coordinated schedunng / beamfoming (CS / CB).

 The JR scheme means that a signal transmitted through a PUSCH is received at a plurality of reception points, and the CS / CB scheme means that a PUSCH is received only at one point, but user scheduling / beamforming is a function of cells of a CoMP cooperative unit. Means determined by the adjustment.

 [123] CSI-RS configuration

 As described above, in the LTE-A system supporting up to eight transmit antennas in the downlink, the base station should transmit CSI-RSs for all antenna ports. Transmitting CSI-RS for up to eight transmit antenna ports every subframe has a significant disadvantage, so CSI-RS should be transmitted intermittently on the time axis rather than every subframe. Reduce head Accordingly, the CSI 'RS may be transmitted periodically with a period of one subframe any integer multiple or may be transmitted in a specific transmission pattern.

At this time, the period or pattern in which the CSI-RS is transmitted may be configured by the base station. In order to measure the CSI-RS, the UE must know the CSI—RS configuration for each CSI-RS antenna port of the cell to which the UE belongs. In the CSI-RS configuration, a downlink subframe index in which the CSI-RS is transmitted and a time ᅳ frequency position of the CSI-RS resource element (RE) in the transmission subframe (for example, FIGS. CSI-RS pattern, as shown in e), and CSI-RS sequence (a sequence used for CSI-RS purposes, according to a predetermined rule based on slot number, cell ID, CP length, etc.). randomly generated), and the like. That is, a plurality of CSI-RS configurations may be used in a given base station, and the base station may inform a CSI-RS configuration to be used for terminal (s) in a cell among the plurality of CSI-RS configurations. [126] addition; Since the CSI-RS for each antenna port needs to be distinguished, resources to which the CSI-RS for each antenna port is transmitted should be orthogonal to each other. As described with reference to FIG. 8, the CSI-RSs for each antenna port may be multiplexed in FDM, TDM and / or CDM scheme using orthogonal frequency resources, orthogonal time resources, and / or orthogonal code resources. Can be.

 [127] Band 1 for the BS to inform UEs in a cell of CSI-RS information (CSI-RS configuration (conf igurat ion)). First, information about a time-frequency to which CSI-RS is mapped to each antenna port. Should you let me know. Specifically, the time information includes subframe numbers through which CSI-RSs are transmitted, periods during which CSI-RSs are transmitted, subframe offsets through which CSI-RSs are transmitted, and CSI-RS resource elements (RE) of specific antennas. The transmitted 0FDM symbol number may be included. The information about the frequency may include frequency spacing in which the CSI-RS resource element (RE) of a specific antenna is transmitted, an offset or shift value of the RE in the frequency axis, and the like.

 9 is a diagram for explaining an example of a method in which a CSI-RS is transmitted periodically. CSI—RS may be transmitted periodically with an integer multiple of one subframe (eg, 5 subframe periods, 10 subframe periods, 20 subframe periods, 40 subframe periods, or 80 subframe periods). .

9 illustrates that one radio frame includes 10 subframes (subframe numbers 0 to 9). In FIG. 9, for example, a case where a transmission period of a CSI-RS of a base station is 10 ms (ie, 10 subframes) and a CSI-RS transmission offset is 3 is illustrated. The offset value may have a different value for each base station so that the CSI-RS of several cells may be evenly distributed in time. When the CSI-RS is transmitted in a period of 10 ms, the offset value may be one of 0 to 9. Can have Similarly, for example, when the CSI-RS is transmitted in a period of 5 ms, the offset value may have one of 0 to 4, and when the CSI—RS is transmitted in the period of 20 ms, the offset value is one of 0 to 19. The offset value may have one of 0 to 39 when the CSI-RS is transmitted in a period of 40 ms. The offset value may be 0 to 79 when the CSI-RS is transmitted in a period of 80 ms. It can have one value. This offset value indicates the value of the subframe where the base station transmitting the CSI-RS in a predetermined period starts the CSI-RS transmission. When the base station informs the transmission period and the offset value of the CSI—RS, the terminal can receive the CSI-RS of the base station at the corresponding subframe location by using the value. The terminal measures the channel through the received CSI-RS and As a result, information such as CQI, PMI and / or Rank Indicator (RI) can be reported to the base station. Except where CQI, PMI, and RI are distinguished and described herein, these may be collectively referred to as CQI (or CSI). In addition, the CSI-RS transmission period and offset may be separately designated for each CSI-RS configuration.

 FIG. 10 is a diagram for explaining an example of a method in which a CSI-RS is transmitted aperiodically. In FIG. 10, one radio frame includes 10 subframes (subframe numbers 0 to 9). As shown in FIG. 10, the subframe in which the CSI-RS is transmitted may appear in a specific pattern. For example, the CSI-RS transmission pattern may be configured in 10 subframe units, and whether or not to transmit CSI-RS in each subframe may be designated as a 1-bit indicator. 10 illustrates a CSI-RS pattern transmitted at subframe indexes 3 and 4 within 10 subframes (subframe indexes 0 to 9). Such an indicator may be provided to the terminal through higher layer signaling.

 The configuration for CSI-RS transmission may be configured in various ways as described above. In order for the terminal to correctly receive the CSI-RS and perform channel measurement, the base station may configure the CSI-RS. I need to tell the terminal-. Embodiments of the present invention for informing the UE of the CSI-RS configuration will be described below.

 [132] How to Tell CSI-RS Settings

 In general, the following two methods may be considered as a method of informing the UE of a CSI-RS configuration.

 The first method is a method in which a base station broadcasts information on a CSI-RS configuration to terminals by using dynamic broadcast channel (DBCH) signaling.

In the existing LTE system, when the base station informs the UE about the system information, the information can be transmitted through a normal BOKBroadcasting channel). If there is a lot of information about the system information to inform the terminal and cannot transmit all by BCH alone, the base station transmits the system information in the same manner as general downlink data, but the PDCCH CRC of the heading-data is determined using a specific terminal identifier (for example, For example, system information may be transmitted by masking using a system information identifier (SI ᅳ RNTI) rather than a C-RNTI. In this case, the actual system information is transmitted on the PDSCH region like general unicast data. Accordingly, all terminals in the cell decode the PDCCH using SI-RNTI, System information may be obtained by decoding the PDSCH indicated by the corresponding PDCCH. Such a broadcasting method may be referred to as a dynamic BCH (DBCH) by being distinguished from a physical broadcasting (PBCH) which is a general broadcasting method.

 Meanwhile, system information broadcast in the existing LTE system can be largely divided into two types. One of them is a master information block (MIB) transmitted through a PBCH, and the other is a system information block (SIB) transmitted by being multiplexed with general unicast data on a PDSCH region. Since information transmitted as SIB type 1 to SIB type 8 (SIB1 to SIB8) is defined in an existing LTE system, information about CSI-RS configuration, which is new system information not defined in the existing SIB type, is defined. You can define a new SIB type. For example, by defining the SIB9 or SIB10 and through this information about the CSI-RS configuration (base station) can be informed to the UEs in the cell in the DBCH method DB.

 The second method is a method in which a base station informs each terminal of information on CSI—RS configuration using Radio Resource Control (RRC) signaling. That is, information on the CSI-RS configuration may be provided to each of the terminals in the cell by using dedicated RRC signaling. For example, in a process of establishing a connection ion with a base station through initial access or handover, the base station may inform the terminal of CSI—RS configuration through RRC signaling. Can you-. Alternatively, when the base station transmits an RRC signaling message requesting channel state feedback based on the CSI-RS measurement to the terminal, the base station may inform the terminal of the CSI—RS configuration through the corresponding RRC signaling message.

 [138] Indication of CSI-RS Settings

[139] may be a plurality of CSI-RS settings (configuration) is used in any base station, the base station may transmit to the mobile ^station, over a predetermined sub-frame according to the CSI-RS each CSI-RS configuration. In this case, the base station informs the user equipment of a plurality of CSI-RS configuration, and among them, informs the user equipment of the CSI—RS to be used for channel state measurement for CQKChannel Quality Information or CSI (Channel State Information) feedback. You can enjoy it. ^' [140] ^non-, as the di-base for explaining an example of what to CSI-RS settings (configuration) and instruction (indication) the channel measurement Ke CSI- RS to be used to be used in the terminal aeseo below.

 FIG. 11 is a diagram for explaining an example in which two CSI-RS configurations (conf igurat ion) are used. In FIG. 11, one radio frame includes 10 subframes (subframe numbers 0 to 9). In FIG. 11, the first CSI—RS configuration, that is, the CSI-RS1 has a CSI-RS transmission period of 10 ms and a CSI-RS transmission offset of 3 IDs. In FIG. 11, the second CSI-RS configuration, that is, the CSI-RS2 has a CSI-RS transmission period of 10 ms and a CSI-RS transmission offset of 4 bytes. The base station informs the user equipment about two CSI-RS configuration (conf igurat ion), and can inform which of these CSI-RS configuration (conf igurat ion) to use for CQI (or CSI) feedback.

 [142] When the UE receives a request for CQI feedback from a base station from a CSI-RS configuration (conf igurat ion), the UE performs channel state measurement using only the CSI-RS belonging to the CSI-RS configuration (conf igurat ion). can do. Specifically, the channel state is determined as a function of the CSI—RS reception quality and the amount of noise / interference and the correlation coefficient. The CSI—RS reception quality measurement is performed using only the CSI-RS belonging to the corresponding CSI-RS configuration. In order to measure the amount of noise / interference and the correlation coefficient (e.g., an interference covariance matrix indicating the direction of the interference, etc.), the measurement is performed in the corresponding CSI-RS transmission subframe or in designated subframes. Can be. For example, in the embodiment of FIG. 11, when the UE receives a request for feedback from the base station from the first CSI-RS configuration (CSI—RSI), the UE receives a fourth subframe (subframe index 3) of one radio frame. The CSI-RS is used to measure reception quality, and can be specified to use odd-numbered subframes separately for measuring noise / interference and correlation coefficients. Alternatively, the CSI-RS reception quality measurement and the amount of noise / interference and the correlation coefficient measurement may be specified to be limited to a specific single subframe (eg, subframe index 3).

For example, the received signal quality measured using the CSI-RS is simply a signal-to-interference plus noise ratio (SINR) as S / (I + N) ( Where S is the strength of the received signal, I is the amount of interference, and N is the amount of noise. S may be measured through the CSI-RS in the subframe including the CSI-RS in the subframe including the signal transmitted to the UE. I and N are the amount of interference from neighboring cells, Since the signal is changed according to the direction of the signal from the neighboring cell, it can be measured through a CRS transmitted in a subframe for measuring s or a subframe designated separately.

 Here, the measurement of the amount of noise and interference and the correlation coefficient may be performed at a resource element (RE) to which the CRS or CSI-RS is transmitted in the corresponding subframe, or the measurement of noise / interference may be performed. This may be done through a null RE element configured to facilitate this. In order to measure noise / interference in the CRS or CSI-RSRE, the UE first recovers the CRS or CSI-RS, and then subtracts the result from the received signal, leaving only the noise and interference signal, and thereby removing the noise. You can get statistics of interference. Null RE means a RE that the base station is empty without transmitting any signal (that is, transmit power is zero), and facilitates signal measurement from other base stations except the base station. CRSRE, CSI-RS RE, and Null RE may all be used to measure the amount of noise / interference and the correlation coefficient, but the base station may designate to the terminal as to which of these REs to measure the noise / interference. .have. This is because, depending on whether the signal of the neighbor cell transmitted to the RE location where the UE performs the measurement is a data signal or a control signal, it is necessary to appropriately designate the RE to be measured by the UE. What is the signal of the neighboring cell is different depending on whether the synchronization between the cells and the CRS configuration (configuration) and CSI-RS configuration (configuration), so that the base station can determine the RE to perform the measurement by identifying this. . That is, the base station can designate the terminal to measure noise / interference using all or part of CRS RE, CSI-RS RE and Null RE.

For example, the base station may use a plurality of CSI-RS configuration, and the base station informs the terminal of one or more CSI-RS configuration, and among them, the CSI- to be used for CQI feedback. It can tell you about RS configuration and Null RE position. The CSI-RS configuration to be used for CQI feedback by the terminal is expressed in terms of distinguishing it from a null RE transmitted with a transmission power of 0, which is a CSI-RS configuration transmitted with a non-zero transmission power. configuration). For example, the base station informs one CSI-RS configuration at which the terminal will perform channel measurement, and the terminal is non-zero in the one CSI-RS configuration. It can be assumed to be transmitted at the transmit power. In addition, the base station may be configured for a CSI-RS configuration transmitted with a transmission power of zero. (Ie, about a Null RE location), the UE may assume that the transmission power is 0 with respect to the resource element (RE) location of the corresponding CSI-RS configuration. In other words, the base station informs the terminal of one CSI-RS configuration () 11 ^^^ 01 of a transmission power other than zero, and if there is a CSI-RS configuration of 0 transmission power. May inform the terminal of the corresponding null RE position.

 [146] As an alternative to the indication scheme of the same CSI-RS configuration, the base station informs the CSI-RS configuration of a plurality of terminals, among which all or part of it is used for CQI feedback. It can tell you about the CSI-RS configuration. Accordingly, the UE, which has received CQI feedback on a plurality of CSI-RS configurations, measures CQIs using CSI-RSs corresponding to the CSI-RS configurations, and measures the measured CQIs. Information can be sent together to the base station.

 Or, the base station can transmit the uplink resources required for the CQI transmission of the terminal for each CSI-RS configuration so that the terminal can transmit the CQI for each of a plurality of CSI ᅳ RS configuration (base station) The uplink resource designation may be specified in advance and may be provided to the terminal in advance through RRC signaling.

 Alternatively, the base station may dynamically trigger the terminal to transmit CQI for each of a plurality of CSI—RS configurations to the base station. Dynamic triggering of CQI transmission may be performed through the PDCCH. Which CSI-RS configuration (CQI) measurement to be performed may be known to the UE through the PDCCH. The UE receiving the PDCCH may feed back a CQI measurement result for the CSI ᅳ RS configuration specified in the corresponding PDCCH to the base station.

A transmission time of a CSI-RS corresponding to each of a plurality of CSI-RS configurations may be specified or transmitted in another subframe, or may be specified to be transmitted in the same subframe. When transmission of CSI-RSs according to different CSI-RS configurations is designated in the same subframe, it is necessary to distinguish them from each other. In order to distinguish CSI-RSs according to different CSI-RS configurations, one or more of time resources, frequency resources, and code resources of a CSI-RS transmission may be differently applied. For example, in the corresponding subframe, the transmission RE position of the CSI-RS is different for each CSI-RS configuration (for example, the CSI-RS according to one CSI-RS configuration is the RE position of FIG. 8 (a)). Is transmitted from, and the CSI-RS according to another CSI-RS configuration is the same In one subframe, it can be specified to be transmitted in the RE position of FIG. 8 (b) (division using time and frequency resources). Alternatively, when CSI-RSs according to different CSI-RS configurations are transmitted from the same RE location, the CSI-RS scrambling codes are differently used in different CSI-RS configurations to distinguish them from each other. You can also do this (code division).

 [150] Method of calculating channel state information in CoMP system

 Hereinafter, a method of determining the overhead of the band 1 and the CRS that the terminal receives the CSI-RS to calculate the channel state information (eg, the CQI) will be described in detail.

 In a CoMP system, when a terminal measures a channel from a CRS based on a cell identifier between a plurality of transmission points sharing the same cell identifier (ID), there is a problem in that a channel of each transmission point cannot be distinguished. This is because a plurality of transmission points sharing the same cell identifier simultaneously transmit the same CRS, and at this time, a channel measured from the CRS becomes one channel in which channels of the plurality of transmission points are combined. Therefore, in order for the UE to measure the independent channel of each transmission point, it is efficient to measure the CSI-RS transmitted for each transmission point.

 Even when channel reversibility is used in a TDD CoMP system, it is effective to use the above-described CSI-RS based channel measurement method. If channel reversibility exists, the base station may estimate some information of the downlink channel using an uplink sounding reference signal (SRS). Specifically, the base station may estimate the RI or PMI information of the channel state information from the SRS without feedback of the terminal. However, even in this case, the CQI of the channel state information is difficult to be estimated from the SRS due to the channel difference between the downlink and the uplink. Therefore, in the TDD> ΜΡ system, the terminal must transmit the CQI to the base station. In this case, as described above, the CQI may be generated based on the CSI-RS, not the CRS, to distinguish channels of transmission points sharing the same cell identifier.

That is, in the TDD CoMP system, the base station may be configured not to report the RI and the PMI to the terminal, and may be configured to calculate the CQI based on the CSI ᅳ RS corresponding to each transmission point. In general, when the UE calculates the CQI, the UE assumes the CRS overhead of the corresponding cell and determines that the data signal is not transmitted from the RE to which the CRS is transmitted. However, when the terminal calculates the CQI based on the CSI—RS, the terminal transmits any of a plurality of transmission points. Since it is not known whether the CSI-RS has been received from the point, the method of determining the CRS overhead becomes a problem. For example, if the CSI-RS received by the UE is the CSI-RS of the serving transmission point, the CQI may be calculated assuming CRS overhead corresponding to the CRS of the serving transmission point, but the CSI—RS received by the terminal If CSI-RS is a non-serving transmission point, how to determine the CRS overhead for CQI calculation is a problem.

 According to the present invention, when the UE calculates and feeds back the CQI based on the CSI-RS without reporting the PMI and the RI, the UE may determine the CRS overhead according to the following embodiments.

 As a first embodiment, the UE may determine the CRS overhead according to the number of ports of the CSI-RS used to calculate the CQI based on the CSI-RS. That is, when the terminal calculates the CQI using the N port CSI-RS, it is assumed that the CRS overhead of the N port.

 For example, when the CSI-RS of one port is configured in the terminal, the terminal calculates the CQI by assuming a CRS overhead corresponding to the CRS of one port. That is, the terminal assumes that the number of ports of the CRS is 1 because the number of ports of the CSI RS is 1, and calculates the CQI based on the CRS overhead of one port.

 In addition, when the CSI-RS of the two ports are configured in the terminal, the terminal calculates the CQI assuming CRS overhead corresponding to the CRS of the two ports. That is, since the number of ports of the CSI RS is 2, the terminal assumes the number of ports of the CRS to be 2, and calculates the CQI based on the CRS overhead of the two ports.

 In addition, when the 4-port CSI-RS is configured in the terminal, the terminal calculates the CQI assuming a CRS overhead corresponding to the 4-port CRS. In other words, since the number of ports of the CSI RS is 4, the terminal assumes the number of ports of the CRS as 4, and calculates the CQI based on the CRS overhead of 4 ports.

 On the other hand, when the CSI-RS of the N port is set, but the transmission mode for the antenna of the N port does not exist, the terminal assumes the transmission mode of a specific M (M <N) port of the N port M port The CQI may be calculated based on the CRS overhead of.

For example, in a current LTE system (for example, release 8), if there is a maximum of 4 ports of CRS, assuming CRS overhead of up to 4 ports, CQI may be calculated. Specifically, when the 8 port CSI-RS is configured in the terminal, the terminal may calculate the CQI assuming CRS overhead of the 4 port CRS. Transmission Mode for 8-Port Antenna Since the terminal does not exist, the terminal assumes a transmission mode using only four of eight ports.

 In case of calculating the CQI according to the first embodiment, the UE may use the CQI calculation method of transmission mode 2 in the current LTE system (eg, release 8). In transmission mode 2, the channel is estimated from the CRS, and when the CRS port is M, the CQI is calculated assuming a downlink transmission method using the M port. At this time, it is assumed that the CRS overhead is the CRS overhead of the M-foam. Similarly, when the CQI is calculated using the CSI-RS port of the N port in the present invention, the CRS overhead may be determined by assuming that the number of CSI-RS ports is the number of CRS ports. That is, the CQI can be calculated assuming the CRS overhead of the N port. According to the first embodiment, the complexity of the UE implementation can be reduced by using the CQI calculation method of TM2.

 As a second embodiment, when the UE calculates the CQI based on the CSI-RS, the UE may calculate the CQI by assuming a CRS overhead corresponding to the CRS port of the serving transmission point. That is, when the CSI-RS of the N port is set in the terminal and the number of CRS ports of the serving transmission point is M, the terminal calculates the CQI assuming the CRS overhead of the M port regardless of the number of ports of the CSI-RS. .

 In the example, when the CSI-RS of one port is set in the terminal and the number of CRS ports of the serving transmission point is 2, the terminal calculates the CQI assuming CRS overhead of the two ports. That is, the UE calculates the CQI based on the CRS overhead of two ports according to the number of CRS ports of the serving transmission point regardless of the number of CSI-RS ports.

 In addition, when CSI-RS of 2 ports is configured in the terminal and the number of CRS ports of the serving transmission point is 4, the UE calculates CQI by assuming CRS overhead of 4 ports. That is, the UE calculates the CQI based on the C S overheads of four ports according to the number of CRS ports of the serving transmission point regardless of the number of CSI-RS ports.

 On the other hand, if there is no transmission mode for the N-port antenna, the UE calculates the CQI assuming a transmission mode using only a specific M (M <N) port among the N ports. For example, since there are up to four ports of CRS in the current LTE system (eg, Release 8), the CQI can be calculated assuming a maximum of four ports of CRS overhead.

According to the second embodiment-when calculating the CQI, the UE can determine the CRS overhead through a relatively simple procedure compared to the first method. 12 is a flow diagram illustrating a merged CSI feedback method according to an embodiment of the present invention.

 First, the terminal receives the CSI configuration information from the base station (S1210).

 As described above, the terminal may receive the CSI configuration information for the period or pattern in which the CSI-RS is transmitted from the base station. In order to measure CSI-RS, the UE must know the CSI-RS configuration for each CSI-RS antenna port of the cell to which it belongs. The base station may transmit the CSI configuration information to the terminal through higher layer signaling (eg, RRC signaling).

 Next, the terminal receives the CSI-RS according to the CSI configuration information (S1230).

 As described above, CSI 'RS is one of RSs newly introduced in LTE—A system. The CSI-RS is an RS for channel measurement for selecting a transmission tank, a modulation and coding scheme (MCS), a precoding matrix index (PM I), and the like. Each of the plurality of transmission points sharing the cell identifier transmits CSI ᅳ RS through different resources.

 Next, the UE determines the overhead of a common reference signal (CRS) resource element based on the number of antenna ports equal to the number of antenna ports associated with CSI—RS (S1250).

 As described above, since the UE calculates the CQI based on the CSI-RS, the UE cannot know which of the plurality of transmission points the CSI-RS is received from,

The problem is how to determine the CRS overhead.

 As a first embodiment, the UE can calculate the CQI based on the CSI-RS, and may determine the CRS overhead according to the number of ports of the CSI-RS used for the CQI calculation. That is, when the terminal calculates the CQI using the N port CSI-RS, it is assumed that the CRS overhead of the N port.

 As a second embodiment, when the UE calculates the CQI based on the CSI-RS, the UE may calculate the CQI by assuming a CRS overhead corresponding to the CRS port of the serving transmission point. That is, when the CSI-RS of the N port is set in the terminal and the number of CRS ports of the serving transmission point is M, the terminal calculates the CQI assuming CRS overhead of the M port regardless of the number of ports of the CSI-RS.

 Next, the terminal transmits the channel state information calculated based on the overhead of the CSI—RS and CRS resource elements (S1270).

[178] Figure 13 illustrates a base station and a terminal that can be applied to an embodiment of the present invention. When a relay is included in the wireless communication system, communication is performed between the base station and the relay in the backhaul link, and communication is performed between the relay and the terminal in the access link. Therefore, the base station or the terminal illustrated in the figure may be replaced with a relay according to the situation.

 Referring to FIG. 13, a wireless communication system includes a base station 1310 and a terminal 1320. The base station 1310 includes a processor 1313, a memory 1314, and a radio frequency (RF) unit 1311, 1312. The processor 1313 may be configured to implement the procedures and / or methods proposed by the present invention. The memory 1314 is connected with the processor 1313 and stores various information related to the operation of the processor 1313. The F unit 1316 is connected with the processor 1313 and transmits and / or receives a radio signal. The terminal 1320 includes a processor 1323, a memory 1324, and RF units 1321 and 1322. The processor 1323 may be configured to implement the procedures and / or methods proposed by the present invention. The memory 1324 is connected with the processor 1323 and stores various information related to the operation of the processor 1323. The RF units 1321 and 1322 are connected to the processor 1323 and transmit and / or receive a radio signal. The base station 1310 and / or the terminal 1320 may have a single antenna or multiple antennas.

 The embodiments described above are those in which the components and features of the present invention are combined in a predetermined form. Each component or feature is to be considered optional unless stated otherwise. Each component or feature may be embodied in a form that is not combined with other components or features. It is also possible to combine some components and / or features to constitute an embodiment of the invention. The order of the operations described in the embodiments of the present invention may be changed. Some components or features of one embodiment may be included in another embodiment, or may be replaced with corresponding components or features of another embodiment. It is obvious that the claims may be combined with claims that do not have an explicit citation in the claims, or may be incorporated into new claims by post-application correction.

In this case, the specific operation described as performed by the base station may be performed by an upper node in some cases. That is, it is obvious that various operations performed for communication with a terminal in a network including a plurality of network nodes including a base station may be performed by the base station or network nodes other than the base station. Iii. A base station may be replaced by terms such as a fixed station, Node B, eNc) deB (eNB), an access point, and the like. The embodiment according to the present invention may be implemented by various means, for example, hardware, firmware, software, or a combination thereof. For implementation in hardware, an embodiment of the present invention may include one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs),. Programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, and the like.

 In the case of implementation by firmware or software, an embodiment of the present invention may be implemented in the form of a module, procedure, function, etc. that performs the functions or operations described above. The software code may be stored in a memory unit and driven by a processor.

 The memory unit may be located inside or outside the processor, and may exchange data with the processor by various known means.

 The foregoing detailed description of the preferred embodiments of the present invention as described above has been provided to enable those skilled in the art to implement and practice the present invention. Although the above has been described with reference to a preferred embodiment of the present invention, those skilled in the art will understand that various modifications and changes can be made without departing from the scope of the present invention. For example, those skilled in the art can use each of the configurations described in the above embodiments in combination with each other. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

 The present invention can be embodied in other specific forms without departing from the spirit and essential features of the present invention. Accordingly, the above detailed description should not be construed as limiting in all aspects and should be considered as illustrative. The scope of the present invention should be determined by reasonable interpretation of the appended claims, and all changes within the equivalent scope of the present invention are included in the scope of the present invention. The present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. In addition, the claims may be incorporated into claims that do not have an explicit citation relationship in the claims, or may be incorporated into new claims by revision after application.

【Industrial Availability】 The present invention can be used in a wireless communication device such as a terminal, a relay, a base station, and the like. -

Claims

[Range of request]

 [Claim 1]

 A method of transmitting channel state information (CSI) by a terminal in a wireless communication system, the method comprising: receiving a channel state information-reference signal (CSI ᅳ RS);

 Determining an overhead of a common reference signal (CRS) resource element based on the same antenna port number as the antenna port number associated with the CSI-RS; And

 Transmitting the channel state information calculated based on the overhead of the CSI-RS and the CRS resource element.

 The channel state information transmission method comprising a.

 [Claim 2]

 According to claim 11,

 And receiving CSI configuration information for reporting the CSI.

 [Claim 3]

 According to claim 2,

 Wherein the CSI configuration information is configured to report a channel quality indicator (CQI) without reporting a precoding matrix indicator (PMI) and a rank indicator (RI).

 [Claim 4]

 The method of claim 2,

 The CSI configuration information is transmitted through RRC (Radio Resource Control) signaling.

 [Claim 5]

 In U,

 And the number of antenna ports associated with the CSI-RS is set to 4 or less.

 [Claim 6]

 In claim 1,

Wherein the CSI indicates a channel state in a Cooperative Multiple Point Time Division (TDD) system that satisfies channel reciprocity. [Claim 71

 In a method of receiving a channel state information (CSI) in a base station in a wireless communication system,

 Transmitting a channel state information-reference signal (CSI-RS); And

 Receiving the channel state information calculated based on the overhead of the CRS resource element and the CSI-RS,

 The overhead of the CRS resource element is determined based on the same number of antenna ports as the number of antenna ports associated with the CSI-RS.

 [Claim 8]

 The method of claim 7,

 And transmitting CSI configuration information for reporting the CSI.

 [Claim 9]

 The method of claim 8,

 The CSI configuration information is configured to report a channel quality indicator (CQI) without reporting a precoding matrix indicator (PMI) and a rank indicator (RI).

[Claim 10]

^'According to claim 8,

 The CSI configuration information is transmitted through RRC (Radio Resource Control) signaling.

 [Claim 11]

 In claim 7

 And the number of antenna ports associated with the CSI-RS is set to 4 or less.

 [Claim 12]

 The method of claim 7,

 Wherein the CSI is indicative of channel status in a Cooperative Multiple Point Time Division (TDD) system that satisfies channel reciprocity.

[Claim 13] In a terminal for transmitting channel state information (CSI) in a wireless communication system,

 RF (Radio Frequency) unit; And

 Including a processor,

 The processor,

 Receives channel status information ᅳ reference signal (CSI-RS),

 Determine an overhead of a common reference signal (CRS) resource element based on the same antenna port number as the antenna port number associated with the CSI-RS,

 The CSI—the UE configured to transmit the channel state information calculated based on an overhead of an RS and the CRS resource element.

 [Claim 14]

 In a base station for receiving channel state information (CSI) in a wireless communication system,

 RF (Radio Frequency) unit; And

 Including a processor,

 The processor is,

 Transmit channel status information-reference signal (CSI-RS),

 Receiving the channel state information calculated based on the overhead of the C S resource element and the CSI-RS,

 The overhead of the CRS resource element is configured to be determined based on the same antenna port number as the antenna port number associated with the CSI-RS.